Twelve experiments investigate the early development, in human infants, of perception of the unity of partly occluded surfaces. The experiments focus on a time during ontogeny when there may be evidence of visual sensitivity to information specifying object properties, but limited ability to perceive occlusion, with the goal of observing real-time processes by which the infant assembles visible parts of a stimulus into a coherent whole. This approach stipulates that onset of sensitivity to motion and orientation information, development of the oculomotor system, and experience viewing objects undergoing occlusion and disocclusion, play a direct, foundational role in the ontogeny of object perception. That is, there is an hypothesized period, 2 to 4 months of age, during which infants come to use newly-emerged visual skills to perceive objects accurately. The experiments follow a similar strategy: explorations of individual and group differences in both basic visual processing skills and perception of the unity of partly occluded surfaces. Infant perception is assessed with two methods: (a) recording of eye movements, to measure improvements in pickup of important visual .information, and (b) habituation/dishabituation, to ascertain perception of object unity as well as to determine the extent of sensitivity to available visual information. It is expected that the detailed analysis of individual differences afforded by this approach provide the opportunity for exceptionally sensitive measures of the emergence of visual skills and object knowledge. The short-term objectives of the present proposal are to elucidate fundamental developmental mechanisms in the context of the classic nature-nurture debate. The long-term goals are to shed light on the larger question of how knowledge is acquired and structured in the human, and how perceptual skills impact knowledge acquisition and structure. In the future, such understanding may aid in the formulation of diagnostics and treatments for some developmental disorders.